The prior art is filled with numerous examples of pressure transducers. Diaphragm based pressure transducers convert applied pressure into stresses in the plane of the diaphragm. These stresses can be conveniently measured and converted into electrical signals by the use of piezoresistive sensors or other strain gauge devices which are mounted on or which are part of the diaphragm. A common arrangement is that of a clamped edge diaphragm wherein the outer portion of the diaphragm is fixed and a central region deflects under applied pressure. In conventional terminology the central region which constitutes a diaphragm region is referred to as the active region. In a conventional clamped diaphragm, the stress on the surface of the diaphragm varies from a maximum tensile stress at the clamped edges to a maximum compressive stress in the center of the diaphragm. Such diaphragms can be made of metal to which sensors are cemented or in other cases from a semiconductor material such as silicon on which the sensors are either embedded or affixed.
The operation of such diaphragms as well as the stresses that incur in such diaphragms have been widely explained. See for example, U.S. Pat. No. 5,614,678, entitled “High Pressure Piezoresistive Transducer”, issued Mar. 25, 1997 to A. D. Kurtz et al. an inventor herein and assigned to Kulite Semiconductor Products, Inc., the assignee herein. Many prior art pressure transducers utilize metal diaphragms where the sensors are cemented or otherwise secured to the metal diaphragms. Such devices are capable of operating at extremely high pressures. For example, such pressures can be between 15,000 and 30,000 psi or higher. Other devices in the prior art show high pressure transducers which incorporate metal diaphragms whereby the transducer is an oil filled pressure transducer. See for example U.S. Pat. No. 4,406,993, entitled “Oil Filled Pressure Transducer” issued on Sept. 27, 1983, to A. D. Kurtz and assigned to the assignee herein.
Thus, as one can ascertain from the prior art there are employed high pressure transducers which utilize metal diaphragms. There transducers are capable of operating at extremely high pressures, but such pressures of operation are below about 60,000 psi. The prior designs were based on a Wheatstone bridge configuration. Such a bridge can sense positive and negative stresses to complete a full bridge design. A Wheatstone bridge was fabricated by placing gages or sensors of the center and outer edges of the diaphragm. Pressure measurements at or above about 60,000 psi provide a problem in regard to operation. At such high pressures when employing a metal diaphragm, the diaphragm thickness increases considerably. In fact, the diaphragm becomes so thick that it can only respond to positive stresses and therefore only positive strain gauges can be employed. With only positive stresses, only a half-bridge design can be utilized. A half-bridge consists of two piezoresistors whereby fixed resistors can also be employed to complete a full Wheatstone bridge. In any event, a half-bridge has significant losses in output and accuracy. The prior art, when operating at such high pressure required the use of only a half bridge design, thus resulting in lower accuracy and lower output.
Certain prior art devices also used transducers and diaphragm constructions which basically had an H shape cross-sectional configuration. Such a configuration has certain advantages in regard to handling as well as mounting of the device. See for example, U.S. Pat. No. 3,739,315, entitled “Semiconductor Transducer Having H Shape Cross-sectional Configuration” by A. D. Kurtz et al. and assigned to Kulite Semiconductor Products, Inc., the assignee herein, and issued on Jun. 12, 1973.